1. Field of the Invention
The present invention relates to a horn switch mechanism mounted on a steering wheel of an automobile.
2. Description of the Prior Art
A known horn switch mechanism of this type is disclosed in Japanese Utility Model Laid-Open Publication No. 57-157569. As reillustrated in FIGS. 1 and 2 of the accompanying drawings, the disclosed switch mechanism is disposed on the top of a boss of the steering wheel. The switch mechanism includes a stationary contact plate 3 in the form of a boss plate 2 made of a steel plate and connected integrally to the boss which is mounted on a steering shaft (not shown), and a movable contact plate 4 made of a steel plate held by a horn pad 1 therein and disposed above the stationary contact plate. The boss plate 2 constitutes a part of a metal core member of the boss.
The stationary contact plate 3 is electrically connected to a negative terminal of a horn control circuit (not shown), and has a plurality of contact points 3a and a plurality of threaded holes 3b at predetermined positions.
The movable contact plate 4 is electrically connected to a positive terminal of the control circuit and has a plurality of downwardly (in FIG. 1) protruded portions defining contact points 4a each in registry with the corresponding contact points 3a. The movable contact plate 4 also has a plurality of insertion bores 4b each in registry with a corresponding threaded hole 3b. A pair of lateral bores or windows 4c, 4c are disposed in the movable contact plate 4 peripherally of each insertion bore 4b.
A cylindrical or tubular retainer clip 5 of a synthetic resin has a pair of locking legs 5a, 5a which are inserted upwardly through the windows for locking engagement with the movable contact plate 4. A coil spring 6 is retained by the retainer clip 5 and disposed between the clip and the stationary contact plate 3 so as to urge the movable contact plate 4 to move upwardly away from the stationary contact plate 3. The retainer clip 5 has locking studs 5b each having a downwardly slanted surface for holding an upper end of the coil spring 6.
A flanged spacer 7 of synthetic resin, having a flange 7a at its upper end, is inserted downwardly through the insertion bore 4b of the movable contact plate 4 and through the retainer clip 5, and is secured to the stationary contact plate 3 by a screw 8 threaded downwardly into a threaded hole 3b of the stationary contact plate 3 through the retainer clip 5. The flange 7a of the flanged spacer 7 is held in engagement with an upper surface of the movable contact plate 4 peripherally of the insertion bore 4b, thereby restricting upward movement of the movable contact plate 4 away from the stationary contact plate 3 and hence, the distance of the space therebetween.
In operation, the horn pad 1 is pressed down by the operator or driver of the car, whereupon the movable contact plate 4 is moved downwardly along the shaft of the flanged spacer 7 against the bias force of the coil spring 6. At this time, the contact point 4a of the movable contact plate 4 is brought into contact with the contact point 3a of the stationary contact plate 3, with the result that the horn control circuit is energized to operate the horn.
In this switch mechanism, the two contact plates 3, 4 are brought into contact with each other at a point disposed remotely from the flanged spacer 7 which serves to guide the vertical movement of the movable contact plate 4. In other words, the two contact points 3a, 4a of the stationary and movable contact plates 3, 4 are located remotely from the flanged spacer 7 along which the movable contact plate 4 is moved down. To this end, the relative location between the contact points 3a, 4a of the two contact plates 3 and 4, and between the threaded hole 3b and the insertion bore 4b, as well as the distance between the contact point 3a and the threaded hole 3b and between the contact point 4a and the insertion bore 4b are controlled with a great precision at the time of assembly of the horn switch mechanism. In addition, it is tedious and laborious to control the relative positions of those contact points 3a, 4a, the threaded hole 3b, and the insertion bores 4b.
The foregoing switch mechanism is also disadvantageous in that a plate portion surrounding the threaded bore 3b of the stationary contact plate 3 has a flat surface, which allows the movable contact plate 4 to be easily displaced sidewardly relative to the stationary contact plate 3 when the screw 8 is inserted through the insertion bore 4b of the movable contact plate 4 for attachment of the spacer to the stationary contact plate 3. This objectionable displacement of the movable contact plate 4 delays the aligning of the two plates because the displaced plate makes it difficult to locate the threaded hole on the stationary plate 3. Thus the attachment thereof requires skill and careful work of the worker.